linux-kernel - Re: [PATCH v3] [RFC] arm: use PSCI if available

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Date:	Thu, 28 Mar 2013 16:00:26 +0000
From:	Will Deacon <will.deacon@....com>
To:	Nicolas Pitre <nicolas.pitre@...aro.org>
Cc:	Rob Herring <robherring2@...il.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"arnd@...db.de" <arnd@...db.de>,
	Marc Zyngier <Marc.Zyngier@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3] [RFC] arm: use PSCI if available

On Thu, Mar 28, 2013 at 03:39:42PM +0000, Nicolas Pitre wrote:
> On Thu, 28 Mar 2013, Rob Herring wrote:
> 
> > On 03/28/2013 09:51 AM, Nicolas Pitre wrote:
> > > On Thu, 28 Mar 2013, Stefano Stabellini wrote:
> > > 
> > >> - the interface to bring up secondary cpus is different and based on
> > >> PSCI, in fact Xen is going to add a PSCI node to the device tree so that
> > >> Dom0 can use it.
> > >>
> > >> Oh wait, Dom0 is not going to use the PSCI interface even if the node is
> > >> present on device tree because it's going to prefer the platform smp_ops
> > >> instead.
> > > 
> > > Waitaminute...  I must have missed this part.
> > > 
> > > Who said platform specific methods must be used in preference to PSCI?
> > 
> > I did. Specifically, I said the platform should be allowed to provide
> > its own smp_ops. A platform may need to do addtional things on top of
> > PSCI for example.
> 
> Then the platform should have its special hook that would override the 
> default PSCI methods.  But, by *default* the PSCI methods should be used 
> if the related DT information is present.

I'm fine with a default PSCI-based implementation, providing that it's actually
a layer between the smp ops and the psci code, not just glueing pointers
together.

KVM and Xen can then use the default implementation, but it does mean that
they have to agree on that interface as it expands in the future. If Xen
relies on the default ops in order to boot, then that's a good incentive not
to deviate from them on the firmware side.

Will
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